Field of the Invention
Embodiments of the invention generally relate to a straddle packer system for use in a wellbore.
Description of the Related Art
A straddle packer system is used to sealingly isolate a section of a wellbore to conduct a treatment operation (for example a fracking operation) that helps increase oil and/or gas production from an underground reservoir that is in fluid communication with the isolated wellbore section. The straddle packer system is lowered into the wellbore on a work string and located adjacent to the wellbore section that is to be isolated. An upper packer of the straddle packer system is actuated into a sealed engagement with the wellbore above the wellbore section to be isolated, and a lower packer of the straddle packer system is actuated into a sealed engagement with the wellbore below the wellbore section to be isolated, thereby “straddling” the section of the wellbore to sealingly isolate the wellbore section from the sections of the wellbore above and below the upper and lower packers.
To conduct the treatment operation, pressurized fluid is supplied down through the work string and injected out of a port of the straddle packer system that is positioned between the upper and lower packers. The upper packer prevents the pressurized fluid from flowing up the wellbore past the upper packer, and the lower packer prevents the pressurized fluid from flowing down the wellbore past the lower packer. The pressurized fluid is forced into the underground reservoir that is in fluid communication with the isolated wellbore section between the upper and lower packers. The pressurized fluid is supplied at a pressure that is greater than the underground reservoir to effectively treat the underground reservoir through which oil and/or gas previously trapped in the underground reservoir can now flow.
After conducting the treatment operation, the straddle packer system can be removed from the wellbore or moved to another location within the wellbore to isolate another wellbore section. To remove or move the straddle packer system, the upper and lower packers first have to be unset from the sealed engagement with the wellbore by applying a force to the straddle packer system by pulling or pushing on the work string that is used to lower or raise the straddle packers system into the wellbore. Unsetting of the upper and lower packers of straddle packer systems, however, is difficult because a pressure differential formed across the upper and lower packers during the treatment operation continues to force the upper and lower packers into engagement with the wellbore after the treatment operation is complete.
The pressure difference is formed by the pressure on the side of the upper and lower packers that is exposed to the pressurized fluid from the treatment operation being greater than the pressure on the opposite side of the upper and lower packers that is isolated from the pressurized fluid from the treatment operation. The pressure differential forces the upper and lower packers into engagement with the wellbore and acts against the force that is applied to unset the upper and lower packers from engagement with the wellbore. Pulling or pushing on the straddle packer system via the work string while the upper and lower packers are forced into engagement with the wellbore either requires a force so large that the force will break or collapse the work string before unsetting the upper and lower packers, or causes the upper and lower packers to move while sealing against the wellbore, also known as “swabbing”, which can tear and damage the upper and lower packers.
Therefore, there is a need for new and improved straddle packer systems and methods of use.